About Subcategories in Navigation

Hello. I have a lot of subcategories that I need to add them in Navigation top menu. So, I have to add all the subcategories as column like this;

http://sv102.piclect.com/92de9ff4e/o/14/09/15/659301.jpg

How can I make the subcategories like that please? This is my site: http://www.arzunet.com

Thanks